Image display devices, such as projectors, rely on the additive properties of light to create colors in displayed images. Such devices generally project light of three or more different wavelengths or wavelength-ranges (such as red, green, and blue) onto a viewing surface in appropriate proportions to create a gamut of many colors perceived by a person viewing the surface (the viewer). However, ambient light also may combine additively with the projected light at the viewer's retina to alter the viewer's color perception of the projected light.
The ambient light may reduce and/or imbalance the gamut of colors perceived by the viewer. For example, displayed colors may be compressed into a reduced gamut, so that colors intended to be distinct are perceived as similar. Differentiating these colors in such a system becomes difficult. Such changes in perceived colors in response to ambient light are termed flare. Colors that are nearer white, that is, high lightness colors, may be more prone to flare, because their perception is more sensitive to any change in the white point of displayed images produced by ambient light. Furthermore, flare tends to be more pronounced in additive color display systems relative to subtractive systems, such as printers.
One approach to correcting color in displayed images may involve sensing the color of ambient light (its white point). The sensed white point of ambient light may suggest a suitable color correction to be applied to the images. Nevertheless, directly sensing the white point may have a number of potential disadvantages. In some cases, simple sensors may be employed to estimate the white point based on a small number of optical measurements. However, these simple sensors may provide a white point estimate that is too inaccurate. Alternatively, more sophisticated sensors may be used to provide a more accurate white point measurement from ambient light. However, these more sophisticated sensors may be too expensive to implement in most image display systems. In addition, even accurate white point information for ambient light may not be sufficient to select a color correction in some cases. For example, light sources with similar white points may have distinct spectral power distributions that interact differently with the surround within a display system.